The MPFL is reconstructed with a free graft and is fixed at the patella with two resorbable knotless anchors to achieve a triangular shaped construct. The loop is then fixed at the correct spot at the femur. Therefore, an eyelet drill wire is inserted in the region of the femoral insertion site and marked.. The entry point of the wire is checked in a strictly lateral image using a fluoroscope. In a previous study, Prof. has proven the insertino area of the MPFL into the femur. This area has been defined as Schoettlel point. This is the most important step of the MPFL reconstruction surgery, If the position of the drill wire is not anatomical, it must be adjusted, as nonanatomic femoral fixation postoperatively can lead to increased patellofemoral pressure or limited range of motion. Once the location of the target wire is physiological, it is overdrilled with a 6mm drill bit to the countercortical bone and the freegraft is fixed.
MPFL - RECONSTRUCTION
The MPFL is the most important passive stabilizer of the patellofemoral joint. Inadequate function plays a crucial role in the development of patellofemoral instability. According to current knowledge, a MPFL rupture or insufficiency is considered a prerequisite for patellofemoral instability. Several studies have shown that in more than 90% of patients who have had patellar dislocation, there is a ruptured or insufficient MPFL. Here, a distinction must be made between an acute, fresh rupture after traumatic dislocation event and a chronic insufficiency or MPFL underdevelopment in patients with already existing habitual patellar luxations. The latter group of patients may be based on a variety of predisposing factors. It is essential to know and consider these when choosing the treatment method. These factors include mainly trochlear dysplasia, patella alta, valgus deformity, internal femur malrotation, and more rarely external tibial rotation. In addition, the localization of the MPFL rupture, patellar or femoral side, plays an important role for estimating the risk of redislocation. Therefore, patient history, clinical examination as well as the diagnostic imaging are decisive in order to determine the presence or the expression of the above mentioned risk factors.
Indication for MPFL reconstruction
An MPFL reconstruction can be performed isolated as well as in combination with other procedures. An isolated MPFL reconstruction is used in patients without any of the above mentioned concomitant pathologies with persistent instability and recurrence dislocations.
In patients with chronic MPFL insufficiency and only mild trochlear dysplasia, the isolated MPFL reconstruction can provide sufficient stabilization of the patella. This is the case in the majority of patients with patellar dislocation.
If there is a trochlear dysplasia more than grade B with a clinical instability between 30 ° and 60 ° knee flexion, the correction of underlying bony pathomorphologies is indicated by the use of a trochleoplasty, creating a trochlear groove for the patella. In addition, an MPFL reconstruction is to be carried out to ensure correct centering of the patella and stability close to extension. However, if the bony bump – present in trochlear dysplasia type C and D – were left, an isolated MPFL reconstruction in dysplastic would led to a massive increase in patellofemoral pressure. This can cause the patient to develop a patellofemoral pain syndrome and significantly accelerate the development of patellofemoral arthrosis.
As already mentioned, isolated MPFL reconstruction is not indicated in patients with patellofemoral arthrosis because it further increases patellofemoral pressure and increases arthrosis. Here, either a transfer of the tuberosity or the surface replacement of the trochlear and, in the case of instability, the following MPFL reconstruction must be considered.
Contraindication for MPFL reconstruction
As mentioned earlier, MPFL reconstruction is not an emergency indication. Individual authors postulate that surgery should be performed at the earliest from the second or third dislocation event. In particular, in planned combination procedures with bony corrections of predisposing factors, a sufficient decongestion, a better range of motion than immediately post-traumatic, and a full resilience should be achieved before surgery.
For a conservative therapeutic trial patients after traumatic patellar dislocation without predisposing concomitant pathology as well as patients after the first event of a patellar dislocation with only mild trochlear dysplasia are eligible. However, the risk of redislocation reported in the literature varies widely and is between 15-44%. This depends strongly on the crack localization of the MPFL. Recent results show that a conservative treatment attempt for patellar outbreaks can lead to good results. The basic prerequisite for a conservative procedure is always the exclusion of osteochondral injuries. Methods include primary suture, refixation of freshly ruptured MPFL with bioresorbable suture anchors, anatomical reconstruction of MPFL with autologous gracile graft, or a “reverse graft” technique with the adductor magnus tendon.
The challenge in the indication for an operative approach is to achieve a sufficient stabilization of the patella, without provoking an increase in pressure on the femoropatellar articular surface. To select the optimal surgical procedure in patients with patella instability, the underlying pathologies must be correctly identified and classified. The following risk factors must be considered:
- triggering event (minor trauma vs chronic habitual patellar luxation without adequate trauma)
- Age at first luxation <14 years
- Instability or dislocation on the opposite side
- Multiple dislocation events
- Positive family history
- Type of trochlear dysplasia
If there is no adequate traumatic event and meet several of the o.g. points to, a higher-grade, static instability with osseous pathomorphology has to be assumed. The risk of redislocation is very high in these cases. Here, the operative stabilization in combination with a correction of the existing accompanying pathology is indicated.
On the way to the process selection for the respective patient, additional information by the clinical investigation as well as the radiological diagnostics are needed:
Evidence of the presence of osseous risk factors in the clinical examination is a valgus position prominent at the standing inspection, a positive apprehension sign at knee flexion above 30 °, and a positive J sign at over 30 ° knee flexion. In particular, the reversed J-sign indicates the presence of a pronounced osseous pathology. This phenomenon describes the insertion of the previously lateralized patella into the trochlea during the transition from extension to flexion, which is achieved by an accustomed trick movement. Likewise, an increased patella shift and tilt is a hint sign. If there is a pronounced patella alta in a patient, this is also clinically recognizable from the outside with a knee flexion of 80°.
If these signs occur during clinical examination, an isolated MPFL reconstruction should not be used.
Another diagnostic criterion is the differentiation between complaints caused by patellofemoral instability and patellofemoral pain. The anterior knee pain often occurs in patients with already existing problems, which may already be preexistent, and may be an indication of an early patellofemoral arthritis.
In these situations, an isolated MPFL reconstruction can lead to an aggravation, since the patellar ridge would possibly be pressed into the already arthritically altered area of the trochlea.
When should an isolated MPFL reconstruction be reconsidered?
The first step is an obligatory MRI assessment to determine the degree of trochlear dysplasia, an eventually increased patellar tilt and shift, and measuring the TTTG. In addition, the condition of the femoropatellar articular cartilage as well as the integrity and rupture area of the MPFS can be estimated. In case of clinical suspicion of a high-grade valgus malalignment and persistent patellofemoral instability over 60 ° knee flexion, whole-legged post-mortem images and, if necessary, a rotation CT must be completed. Thus, the presence of axial deformities can be detected.
If there is a tochlear dysplasia more then grade B with clinical instability between 30 ° and 60 ° knee flexion, the correction of underlying osseous pathomorphology is indicated by the use of a trochleoplasty, creating a trochlear groove for the patella. In addition, an MPFL reconstruction is to be carried out to ensure correct centering of the patella and stability close to extension. However, if the bony bump – present in trochlear dysplasia type C and D – were left, an isolated MPFL reconstruction in dysplastic would led to a massive increase in patellofemoral pressure. This can cause the patient to develop a patellofemoral pain syndrome and significantly accelerate the development of patellofemoral arthrosis.
As already mentioned, isolated MPFL reconstruction is not indicated in patients with patellofemoral arthrosis because it further increases patellofemoral pressure and increases arthrosis. Here, either a transfer of the tuberosity or the surface replacement of the trochlear sleeve bearing and, in the case of instability, the following MPFL plastic must be considered.
Technique in not yet closed / open epiphyseal plates
The femoral MPFL insertion was described by Prof. Schoettle to be distal to the insertion of the adductor magnus muscle and proximal to the MCL and is thus very close to the distal femoral growth groove. However, there are differing opinions as to how the this site is related to the growth plate. In this case, a guide wire is drilled 2-3 mm distal to the medial growth plate in the anterior-posterior beam path and distally in the direction of the knee joint in the area of the point following Schöttle in the lateral beam path. This should be verified in a straight lateral view by fluoroscope, since the insertion site may be falsely proximal due to the non-linear nature of the growth plate.
TROCHLEAR DYSPLASIA / TROCHLEOPLASTY
In high-grade trochlear dysplasia, where the trochlear groove is not only flat but even convex and provided with an additional bump, patellofemoral stability can nit be achieved with an isolated MPFL-reconstruction. Performing an isolated MPFL reconstruction in these cases would increase the pressure on the two joint components, as if pressing one egg on another. Either the MPFL would tear again or it would lead to an early cartilage damage due to an patellofemoral overload. The often recommended transfer of tuberosity can not help either in these cases, since it does not solve the original problem.
Abbildung 22: Technik zur Patellastabilisierung mit Hilfe der Adduktor-magnus-Sehne
In a convex or flat trochlea due to trochlear dysplasia with uncontrollable patellar instability / patellar dislocation, the only anatomical solution is to perform a trochleoplasty where the patellar glide (trochlear groove) is reshaped. This technique, in its meanwhile internationally used form, can be traced back to intensive work of Prof. Schoettle, who uses this technique worldwide (Israel, UAE, USA, CH, F, DEN, RUSSIA, ITALY, SWEDEN, SPAIN, PORTUGAL, ENGLAND, IRELAND, INDIA, JAPAN, BRAZIL, etc.), operates and teaches as a lecturer since 2002. To date, Prof. Schoettle has operated on nearly 1000 trochleoplasties worldwide, which probably gives him the biggest experience in this procedure worldwide. We have published our award-winning results and techniques in international journals and presented them at numerous conferences. In this procedure, the underlying bone is deepened so that it corresponds to the actual anatomy. Trochleoplasty is operated on only during a hospital stay. The hospitalization takes at least 5 days, as we want to ensure that our patients with the newly perceived gait pattern gain confidence as soon as possible. They learn to trust their knee joint and angle it as soon as possible to 60°.
Because of the expected swelling and effusion, we recommend to use crutches for a total of up to 2 weeks. Thereafter, these should be used less as soon as possible. The mobility is, as already mentioned, immediately free from time of the operation and should also be forced.
After the procedure, our patients receive a report which describes the further physiotherapeutic procedure exactly and which should be followed exactly by the follow-up doctor (family doctor, physiotherapist). This includes deliberately light sports activities 6 weeks after the procedure.